This invention relates to an ink jet recording element. More particularly, this invention relates to an ink jet recording element containing porous polymeric particles.
In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An ink jet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-forming layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
While a wide variety of different types of image-recording elements for use with ink jet devices have been proposed heretofore, there are many unsolved problems in the art and many deficiencies in the known products which have limited their commercial usefulness.
It is well known that in order to achieve and maintain photographic-quality images on such an image-recording element, an ink jet recording element must:
Be readily wetted so there is no puddling, i.e., coalescence of adjacent ink dots, which leads to non-uniform density
Exhibit no image bleeding
Absorb high concentrations of ink and dry quickly to avoid elements blocking together when stacked against subsequent prints or other surfaces
Exhibit no discontinuities or defects due to interactions between the support and/or layer(s), such as cracking, repellencies, comb lines and the like
Not allow unabsorbed dyes to aggregate at the free surface causing dye crystallization, which results in bloom or bronzing effects in the imaged areas
Have an optimized image fastness to avoid fade from contact with water or radiation by daylight, tungsten light, or fluorescent light
An ink jet recording element that simultaneously provides an almost instantaneous ink dry time and good image quality is desirable. However, given the wide range of ink compositions and ink volumes that a recording element needs to accommodate, these requirements of ink jet recording media are difficult to achieve simultaneously.
Ink jet recording elements are known that employ porous or non-porous single layer or multilayer coatings that act as suitable image-receiving layers on one or both sides of a porous or non-porous support. Recording elements that use non-porous coatings typically have good image quality but exhibit poor ink dry time. Recording elements that use porous coatings exhibit superior dry times, but typically have poorer image quality and are prone to cracking.
U.S. Pat. Nos. 5,027,131 and 5,194,317 relate to an ink jet recording medium containing polymeric particles in an ink recording layer. However, there is no mention of porous particles.
Japanese Kokai Hei 7[1995]-172037 relates to an ink jet recording sheet containing porous resin particles in an ink recording layer. The preferred multilayered emulsion particles used are disclosed in Japanese Kokai Hei 5[1993]-222108, which teaches that crosslinking monomer in the porous particles should be less than 8%. However, there is a problem with porous particles having a crosslinking monomer of less than 8% in that an ink jet recording sheet containing these particles has poorer dry times, as will be shown hereafter.
Japanese Kokai Hei 2[1990]-127447 relates to transparent plastic sheets containing transparent porous beads which are 4-90 xcexcm in diameter. However, an ink jet recording sheet containing these particles has low gloss, as will be shown hereafter.
Japanese Kokai Hei 2[1990]-55185 relates to a recording material containing a light-transmitting substrate having thereon an ink-transporting layer containing porous particles with a size of 1-30 xcexcm. However, these particles coated on an opaque support will have low gloss, as will be shown hereafter.
It is an object of this invention to provide an ink jet recording element that has a fast ink dry time. It is another object of this invention to provide an ink jet recording element that has high gloss.
These and other objects are achieved in accordance with the invention which comprises an ink jet recording element comprising an opaque support having thereon an image-receiving layer comprising porous polymeric particles in a polymeric binder, the porous polymeric particles having a median diameter of less than about 1 xcexcm and having a degree of crosslinking of about 27 mole % or greater.
Using the invention, an ink jet recording element is obtained which has better dry time and higher gloss than prior art elements while providing good image quality.
As noted above, the support used in the ink jet recording element of the invention is opaque. There may be used, for example, plain papers, resin-coated papers, metal foils, various voided or filled opaque plastics including a polyester resin such as poly(ethylene terephthalate), poly(ethylene naphthalate) and poly(ester diacetate), and the like. The thickness of the support employed in the invention can be from about 12 to about 500 xcexcm, preferably from about 75 to about 300 xcexcm.
The porous polymeric particles which are used in the invention are in the form of porous beads, porous irregularly shaped particles, or are aggregates of emulsion particles.
Suitable porous polymeric particles used in the invention comprise, for example, acrylic resins, styrenic resins, or cellulose derivatives, such as cellulose acetate, cellulose acetate butyrate, cellulose propionate, cellulose acetate propionate, and ethyl cellulose; polyvinyl resins such as polyvinyl chloride, copolymers of vinyl chloride and vinyl acetate and polyvinyl butyral, polyvinyl acetal, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, and ethylene-allyl copolymers such as ethylene-allyl alcohol copolymers, ethylene-allyl acetone copolymers, ethylene-allyl benzene copolymers, ethylene-allyl ether copolymers, ethylene acrylic copolymers and polyoxy-methylene; polycondensation polymers, such as, polyesters, including polyethylene terephthalate, polybutylene terephthalate, polyurethanes and polycarbonates.
In a preferred embodiment of the invention, the porous polymeric particles are made from a styrenic or an acrylic monomer. Any suitable ethylenically unsaturated monomer or mixture of monomers may be used in making such styrenic or acrylic polymer. There may be used, for example, styrenic compounds, such as styrene, vinyl toluene, p-chlorostyrene, vinylbenzylchloride or vinyl naphthalene; or acrylic compounds, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl- a-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; and mixtures thereof In another preferred embodiment, methyl methacrylate is used.
Typical crosslinking monomers used in making the porous polymeric particles used in the invention are aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene or derivatives thereof; diethylene carboxylate esters and amides such as ethylene glycol dimethacrylate, diethylene glycol diacrylate, and other divinyl compounds such as divinyl sulfide or divinyl sulfone compounds. Divinylbenzene and ethylene glycol dimethacrylate are especially preferred. The porous polymeric particles have a degree of crosslinking of about 27 mole % or greater, preferably about 50 mole %, and most preferably about 100 mole %. The degree of crosslinking is determined by the mole % of multifunctional crosslinking monomer which is incorporated into the porous polymeric particles.
The porous polymeric particles used in this invention can be prepared, for example, by pulverizing and classification of porous organic compounds, by emulsion, suspension, and dispersion polymerization of organic monomers, by spray drying of a solution containing organic compounds, or by a polymer suspension technique which consists of dissolving an organic material in a water immiscible solvent, dispersing the solution as fine liquid droplets in aqueous solution, and removing the solvent by evaporation or other suitable techniques. The bulk, emulsion, dispersion, and suspension polymerization procedures are well known to those skilled in the polymer art and are taught in such textbooks as G. Odian in xe2x80x9cPrinciples of Polymerizationxe2x80x9d, 2nd Ed. Wiley (1981), and W. P. Sorenson and T. W. Campbell in xe2x80x9cPreparation Method of Polymer Chemistryxe2x80x9d, 2nd Ed, Wiley (1968).
Techniques to synthesize porous polymer particles are taught, for example, in U.S. Pat. Nos. 5,840,293; 5,993,805; 5,403,870; and 5,599,889, and Japanese Kokai Hei 5[1993]-222108, the disclosures of which are hereby incorporated by reference. For example, an inert fluid or porogen may be mixed with the monomers used in making the porous polymer particles. After polymerization is complete, the resulting polymeric particles are, at this point, substantially porous because the polymer has formed around the porogen thereby forming the pore network. This technique is described more fully in U.S. Pat. No. 5,840,293 referred to above.
A preferred method of preparing the porous polymeric particles used in this invention includes forming a suspension or dispersion of ethylenically unsaturated monomer droplets containing the crosslinking monomer and a porogen in an aqueous medium, polymerizing the monomer to form solid, porous polymeric particles, and optionally removing the porogen by vacuum stripping. The particles thus prepared have a porosity as measured by a specific surface area of about 35 m2/g or greater, preferably 100 m2/g or greater. The surface area is usually measured by B.E.T. nitrogen analysis known to those skilled in the art.
The porous polymeric particles may be covered with a layer of colloidal inorganic particles as described in U.S. Pat. Nos. 5,288,598; 5,378,577; 5,563,226 and 5,750,378, the disclosures of which are incorporated herein by reference. The porous polymeric particles may also be covered with a layer of colloidal polymer latex particles as described in U.S. Pat. No. 5,279,934, the disclosure of which is incorporated herein by reference.
The porous polymeric particles used in this invention have a median diameter of less than about 1 xcexcm, preferably less than about 0.6 xcexcm. Median diameter is defined as the statistical average of the measured particle size distribution on a volume basis. For further details concerning median diameter measurement, see T. Allen, xe2x80x9cParticle Size Measurementxe2x80x9d, 4th Ed., Chapman and Hall, (1990).
As noted above, the polymeric particles used in the invention are porous. By porous is meant particles which either have voids or are permeable to liquids. These particles can have either a smooth or a rough surface.
The polymeric binder used in the invention may comprise a poly(vinyl alcohol), a gelatin, a cellulose ether, polyvinylpyrrolidone, poly(ethylene oxide), etc. The image-receiving layer may also contain additives such as pH-modifiers like nitric acid, cross-linkers, rheology modifiers, surfactants, UV-absorbers, biocides, lubricants, water-dispersible latexes, mordants, dyes, optical brighteners etc.
The image-receiving layer may be applied to one or both substrate surfaces through conventional pre-metered or post-metered coating methods such as blade, air knife, rod, roll, slot die, curtain, slide, etc. The choice of coating process would be determined from the economics of the operation and in turn, would determine the formulation specifications such as coating solids, coating viscosity, and coating speed.
The image-receiving layer thickness may range from about 5 to about 100 xcexcm, preferably from about 10 to about 50 xcexcm. The coating thickness required is determined through the need for the coating to act as a sump for absorption of ink solvent.
Ink jet inks used to image the recording elements of the present invention are well-known in the art. The ink compositions used in ink jet printing typically are liquid compositions comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols. The dyes used in such compositions are typically water-soluble direct or acid type dyes. Such liquid compositions have been described extensively in the prior art including, for example, U.S. Pat. Nos. 4,381,946; 4,239,543 and 4,781,758, the disclosures of which are hereby incorporated by reference.
Although the recording elements disclosed herein have been referred to primarily as being useful for ink jet printers, they also can be used as recording media for pen plotter assemblies. Pen plotters operate by writing directly on the surface of a recording medium using a pen consisting of a bundle of capillary tubes in contact with an ink reservoir.